Holmarc's Contact Angle Meter (Model No: HO-ED-M-01) is a compact and cost effective CMOS based instrument for measuring contact angles of liquids over substrates. Contact angle is the angle formed by a liquid at the phase boundary where a liquid, gas and solid intersect. The shape of the drop is controlled by the three forces of interfacial tension. The shape of a liquid droplet on a flat horizontal solid surface is determined by the Young-Laplace equation. Image Analysis software is used for measurement and further calculations.
The instrument makes use of a CMOS sensor to form the image of the droplet. The CMOS sensor inputs images and live video to a computer for further analysis.
Manual dispensing syringe pump is used for liquid dispensing. The CMOS sensor and imaging optical assembly are mounted on a translation stage for fine adjustment of image position on the sensor. The dispensing system which consists of a syringe along with linear stage is held on a vertical translator for initial setting of the distance of the needle from the solid surface. Back light is provided by bright LED. The illumination intensity of the back light LED can be controlled.
If H represents the protruding height of droplet and D the diameter of the lens, then the contact angle θ is defined by geometry as,
θ = 2 arc tan ( 2H / D )